Wrap spring park brake system, apparatus and method

ABSTRACT

A park brake system for an electric motor actuator is provided. The system may comprise a wrap spring that may rotatably engage the shaft. In this regard, the system may be configured to exert a radial force on a shaft of the electric motor actuator to lock the actuator. Moreover, in various embodiments, the system may be bi-stable.

FIELD

The present disclosure relates to braking systems and, morespecifically, to a bi-stable wrap spring park brake for use with anelectro-mechanical braking system.

BACKGROUND

Typical park brakes or friction brakes consist of a friction disc, whichis clamped via a spring between the brake housing and a steel armatureplate. The armature plate can be manipulated by providing an electricalcurrent pulse to an electro-magnet and permanent magnet assembly inorder to either attract and hold the armature plate away from thefriction disc (free state), or, after reversal of the current pulse,release the armature plate and clamp the friction disc (locked state).These systems are associated with regular maintenance to account forwear and contamination.

SUMMARY

In various embodiments, a park brake system may comprise a rotor cup, amagnet, a stator, a spring and a shaft. The magnet may be operativelycoupled to the rotor cup. The stator may be configured to actuate themagnet in response to an input. The spring may comprise a first end anda second end. The first end may be operatively coupled to the rotor cupand the second end may be operatively coupled to the stator. The springmay be installable around the shaft.

In various embodiments, an electric motor actuator may comprise a shaft,a spring, a rotor cup a magnet, a stator. The spring may be installableon the shaft. The spring may comprise a first spring tang and a secondspring tang. The rotor cup may be rotatably installed about at least aportion of the shaft. The rotor cup may also be configured to receivethe first spring tang. The magnet may be coupled to the rotor cup. Thestator may comprise a coil. The rotor cup may rotate in response to thecoil biasing the magnet. Moreover, the spring may tighten on the shaftin response to the rotor cup rotating in one direction, and loosen onthe shaft in response to the rotor cup rotating in the oppositedirection.

In various embodiments, a method of operating an electric motor actuatorcomprising a park brake system is provided. The method may comprisesteps including: energizing and monitoring an electric motor actuator;detecting a load on the electric motor actuator; energizing an electriccoil assembly in response to the load being above a predeterminedthreshold; and actuating a rotor cup-magnet-stator assembly in responseto energizing the coil, wherein a spring constricts a shaft to lock theelectric motor actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1A illustrates a side cross-sectional view of an electric motoractuator in accordance with various embodiments.

FIGS. 1B-1D illustrate top cross-sectional views of an electric motoractuator in accordance with various embodiments.

FIG. 2 illustrates a perspective cross-sectional view of a portion of anelectric motor actuator in accordance with various embodiments.

FIG. 3 illustrates an exemplary spring in accordance with variousembodiments.

FIG. 4 illustrates various exemplary torque curves of a bi-stableelectric motor actuator in accordance with various embodiments.

FIG. 5A-5D illustrate various perspective views of an exemplary statorassembly and associated components in accordance with variousembodiments.

FIG. 6 is a block diagram that illustrates a method of operating anelectric motor actuator in accordance with various embodiments.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration and their best mode. While these exemplary embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the inventions, it should be understood that other embodimentsmay be realized and that logical, chemical and mechanical changes may bemade without departing from the spirit and scope of the disclosure.Thus, the detailed description herein is presented for purposes ofillustration only and not of limitation. For example, the steps recitedin any of the method or process descriptions may be executed in anyorder and are not necessarily limited to the order presented.

Furthermore, any reference to singular includes plural embodiments, andany reference to more than one component or step may include a singularembodiment or step. Also, any reference to attached, fixed, connected orthe like may include permanent, removable, temporary, partial, fulland/or any other possible attachment option. Additionally, any referenceto without contact (or similar phrases) may also include reduced contactor minimal contact.

As used herein, phrases such as “make contact with,” “coupled to,”“touch,” “interface with” and “engage” may be used interchangeably.Different cross-hatching may be used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

In various embodiments, a brake system may comprise anelectro-mechanical actuator (“EMA”). The EMA may be coupled to orotherwise operate a pressure generating device such as, for example, aball screw, a ram, and/or the like. In operation, the EMA may cause thepressure generating device to move and/or exert a force on other brakesystem structure such as, for example, a brake disk or pad to exert astopping three on a wheel or other suitable moving structure. The brakesystem may also include a park brake feature.

The park brake feature may be used to reduce the load on the EMA whenthe brake is engaged (e.g., in an idle configuration while waiting fortake-off). The park brake feature may also provide brake lockingcapability, when power is not available to maintain power to the EMA(e.g., in a parked configuration).

In various embodiments, FIG. 1A illustrates a side cross-sectional viewof an exemplary EMA 10 and includes a two dimensional x and y forreference and to aid in description. FIG. 1B-1D illustrate topcross-sectional views of an exemplary EMA 10 and includes a twodimensional x and z for reference and to aid in description. EMA 10 maycomprise a shaft 16, stator 20, magnets 30, a rotor cup 40, a bearing50, and a spring 60. Stator 20 may comprise a coil assembly 22. Coilassembly 22 may be housed within stator 20. Bearing 50 may be anysuitable bearing including, for example, a needle bearing and/or anyother suitable bearing and/or bushing.

In various embodiments, spring 60 may comprise one or more spring tangs.For example and as shown in FIG. 1A, spring 60 may comprise a firstspring tang 62 and a second spring tang 64. Spring 60 may furthercomprise a first end associated with first spring tang 62 and/or asecond end associated with second spring tang 64. First spring tang 62may be retained, installed, and/or otherwise captured in a structure ofEMA 10 (e.g., an actuator housing 12 as shown in FIG. 2 and/or othersuitable structure). Second spring tang 64 may be retained, installed,and/or otherwise captured in a structure of EMA 10 (e.g., rotor cup 40and/or other suitable structure).

In various embodiments, spring 60 may be a wrap spring. In this regard,spring 60 may define a channel. Shaft 16 may be installable through thechannel of spring 60. The channel defined by spring 60 may be anysuitable diameter to accommodate shaft 16. In other embodiments, theshaft may receive an intermediate friction element (e.g., a sleeve) thatis rotatably locked with the shaft and engaged by the spring on itsoutside diameter. In various embodiments, spring 60 may be actuatedand/or biased in any suitable direction (e.g., clockwise orcounter-clockwise), to open and/or constrict the channel defined byspring 60. In this regard, spring 60 may be configured to exert a force(e.g., a radial force perpendicular to the x-axis and generally in theplane of the y-axis) on shaft 16. This force may be a binding force. Forexample, this binding force may limit, minimize, and/or prevent motionof shaft 16 under various operating parameters

In various embodiments, magnets 30 may be operatively coupled or affixedto rotor cup 40. Moreover, magnets 30 may be configured to interactmagnetically with stator 20. Rotor cup 40 and stator 20 may befabricated from ferro-magnetic materials and/or more generally, frommaterials with a relative magnetic permeability that is greater thanone. More specifically, stator 20 may be coupled to and/or in electroniccommunication with a power source. In response to the power source beingengaged, stator 20 may create an electromagnetic field that causesmagnets 30 to bias in a direction (e.g., clockwise orcounter-clockwise), as shown in FIG. 1B-1D. Moreover, stator 20 maycomprise one or more mechanical stops (e.g., stop 21, stop 23, and/orthe like). These mechanical stops may be configured to control therotation of magnets 30, rotor cup 40 and/or spring 60 over apredetermined range (e.g., from approximately 15° to approximately 75°as shown in FIGS. 1C and 1D, respectively). To illustrate the rotationalcapability a reference line H (which is included for reference and notas an indication of any associated structure) is included in FIGS.1B-1D, to show the predetermined range defined by the mechanical stop.Moreover, in light of the present disclosure, it should be appreciatedthat the mechanical stops may be installed in an electric motor actuatorsuch that they mechanical stops interact with any number of componentsincluding, for example, stator 20, rotor cup 40, spring 60, and/or thelike. As noted above the second tang 64 of spring 60 may be coupled,attached, and/or installed within rotor cup 40. The actuation of magnets30, which is coupled to rotor cup 40, may cause spring 60 to bias in apre-determined direction.

The quantity and dimensions of magnets 30 (as shown in FIG. 2) may bechosen to produce a magnetic reluctance torque that varies with angularposition. In various embodiments and with reference to FIG. 4, line Iillustrates an exemplary magnetic reluctance torque as a function ofangular position of rotor cup 40 with no current applied to coil 22.Line J shows an exemplary torque as a function of angular portion ofrotor cup 40 with a negative current applied to coil 22. Line K shows anexemplary torque as a function of angular portion of rotor cup 40 with apositive current applied to coil 22. Mechanical stops 421 and 423 arealso shown at exemplary angular positions (e.g., approximately 15° andapproximately 75°) to define a magnetic reluctance torque operatingrange. In this regard, the range of rotational motion of magnets 30 maybe restricted to prevent reaching a position at which both the magneticreluctance as well as the electro-dynamic torques equal zero (e.g.,stable magnetic equilibrium). For example, line L illustrates thecombined torque (e.g., the combined torque illustrated by line I and K)over the operating range defined by mechanical stops 421 and 423 and inresponse to a positive current being applied. Line M illustrates thecombined torque (e.g., the combined torque illustrated by line I and J)over the operating range defined by mechanical stops 421 and 423 and inresponse to a negative current being applied. The number of magnets andthe number of stator teeth may be chosen to be of equal count and sizein order to maximize the achievable reluctance torque and produce at thesame time electro-dynamic torques of sufficient magnitude and polarityto rotate rotor cup 40 (as shown in FIG. 2) from one mechanicallyrestricted position (e.g., a position associated with mechanical stop421) to the opposite mechanically restricted position (e.g., a positionassociated with mechanical stop 423) and back to the first position.

In various embodiments, FIG. 2 shows a perspective cross-sectional viewof a portion of EMA 10 and includes x-y axes for reference. First springtang 62 of spring 60 is coupled to housing 12 (as shown in FIG. 1A).Second spring tang 64 of spring 60 is coupled to rotor cup 40 (as shownin FIG. 1A). As such and in response to magnets 30 being biased and/orrotated by stator 20 (e.g., coil assembly 22 being energized), spring 60engages shaft 16. This engagement causes shaft 16 to be constrained orotherwise prevents or minimizes movement of shaft 16. More specifically,in response to coil 22 being energized and/or powered, magnets 30 arebiased in a direction causing rotor cup 40 to move and creating atorsion force from spring 60 on shaft 16. In this regard, the torsionforce may be created because second tang 64 is coupled to rotor cup 40,which is movable and first tang 62 being coupled to an integral portionof housing 12, which is not movable.

In various embodiments and in response to coil 22 being energized toactuate magnets 30 and/or rotor cup 40, spring 60 is rotated toconstrict, bind, and/or otherwise minimize the motion of shaft 16. Invarious embodiments and with reference to FIGS. 5A-5D, EMA 10 (as shownin FIG. 2) may comprise a stator 20 may be an assembly comprising afirst portion 120 (e.g., a top stator housing) and a second portion 220(e.g., a bottom stator housing). First portion 120 and second portion220 may define a channel or hollow cavity. Coil 22 may be installablein, contained and/or otherwise at least partially surrounded by firstportion 120 and second portion 220. Stator 20 may have a generallycylindrical shape and may have an inner diameter and an outer diameter.Rotor cup 40 and magnets 30 (e.g., magnets 30-1, 30-2, 30-3, 30-4) maybe installable in stator 20 within the inner diameter. EMA 10 maycomprise any suitable number of magnets 30 (e.g., two (2) magnets, four(4) magnets, and/or any suitable number of magnets).

In various embodiments, magnets 30 (e.g., magnets 30-1, 30-2, 30-3,30-4) may be installed or operatively coupled to rotor cup 40 in anysuitable arrangement. More specifically, magnets 30-1, 30-2, 30-3, 30-4may be installed to rotor cup 40 with an alternating North-Southmagnetic pattern. In this regard, the direction of the magnetic fluxemanating from magnets 30 alternates its direction between adjacentmagnets. In order to secure magnets 30 to rotor cup 40, the magnets maybe bonded to rotor cup 40. Magnets 30 may also be retained by a band orsleeve and/or other suitable material with non-magnetic properties thatextends across the outside diameter of magnets 30. In other embodiments,the magnets may also be retained to the rotor by means of mechanicalinterlocking features (e.g., dovetails) or in addition be completelyembedded in epoxy or other suitable non-magnetic formable materials.

In various embodiments, first portion 120 may comprise one or more poleteeth 125 (e.g., north pole teeth 125-1 and 125-2 shown in FIG. 5C).Similarly, second portion 220 may comprise one or more pole teeth 227(e.g., south pole teeth 227-1 and 227-2 shown in FIG. 5D). In variousembodiments, pole teeth 125 and pole teeth 227 may be configured toactuate magnets 30 (e.g., in response to coil 22 being energized). Inthis regard, pole teeth 125 and/or pole teeth 127 may have a flux inresponse to coil 22 being energized. This flux may interact with theflux present in magnets 30 causing magnets 30 to move, as shown in FIG.4.

In response to coil assembly 22 being energized, magnets 30 may beactuated causing rotor cup 40 to be actuated in a first direction (e.g.,clockwise or counter-clockwise). In this regard, spring 60 may also beactuated by virtue of second spring tang 64 being integrally coupledand/or installed in rotor cup 40 to bind and/or otherwise minimizemovement of shaft 16.

In various embodiments, spring 60 may be arranged about shaft 16 suchthat in a free-state (e.g., where spring 60 is not biased), a smallradial clearance between spring 60 and shaft 16 is maintained tominimize friction between spring 60 and shaft 16. Moreover, the winding(e.g., tightening) direction of the spring may be chosen such that the‘tight’ direction or locked-state of spring 60 corresponds with thedirection of rotation of shaft 16 that is associated with the releasedirection of EMA 10. In various embodiments, spring 60 may be wound suchthat the “tight” direction corresponds with the direction ofanti-rotation of shaft 16 in order to bind shaft 16 to create a parkbrake or locked condition.

In various embodiments and with reference to FIG. 3, spring 60 may beany suitable spring. For example, spring 60 may be a wrap spring and/ortorsion spring. Spring 60 may be fabricated from round or square springwire (music or piano wire) or be machined from solid bar stock, ormolded from plastic material. The material of spring 60 may be chosen toachieve corrosion resistance (stainless steel) and sustain itsproperties at low as well as high ambient temperatures ranging fromapproximately −65° F. to 350° F. Spring 60 may have a spring constant ofapproximately 0.05 Nm/rad to approximately 0.5 Nm/rad. In variousembodiments, one or more components (e.g., EMA 10, stator 20, coil 22,and/or the like) may be controlled by or in electronic communicationwith a suitable control unit. The control unit may comprise a processorand a tangible, non-transitory storage medium. The control unit may becapable of monitoring brake and/or EMA 10 operation. The control unitmay further comprise logic that is configured to reduce the load on EMA10 during operation. For example, the control unit may be configured tomonitor a time associated with a load on EMA 10. In response to anelectrical load exceeding a pre-determined threshold (e.g., 20 seconds)the control unit may activate rotor cup 40 and spring 60 to lock EMA 10and minimize the electrical load EMA 10. This condition may occur duringtaxi, as the aircraft is preparing to take off, or as the aircraft ismoving about the airport (e.g., moving to a gate to boarding ordeplaning, moving to a maintenance area, and/or the like). In thisregard, spring 60 may maintain the actuator load after de-energizing EMA10 (park brake mode), and subsequently energizing coil 22 and actuatingrotor cup 40 in the opposite direction to release spring 60 and unlockshaft 16 to remove the actuator load (e.g., service brake mode).

In various embodiments and with reference to FIG. 6, the control unitmay be capable of performing a method to engage and/or disengage a parkbrake in response to detecting an identified condition. The spring maybe kept disengaged from the shaft via magnetic bias of the rotor cupassembly and EMA is free to produce the requested load (Step 610). Morespecifically, upon detecting a desired actuator load, the controller maymaintain power to the EMA such that a constant load is maintained. Inresponse to the load being maintained, the shaft speed is held at ornear zero speed by allowing for occasional motor speed oscillations tooccur. The spring may be maintained in an unwound state (e.g., amechanical clearance between the spring and the shaft is maintained,either by sizing the spring inside diameter and the shaft outsidediameter accordingly, or, by biasing the spring with the help of therotor cup, stator and magnet such that a constant magnetic pull keepsthe spring disengaged from the shaft). In response to the EMA beingcommanded to maintain a pre-selected load, a coil may be energized torotate the rotor cup assembly to tighten the spring in the load releasedirection of the shaft (Step 620). More specifically, in response toenergizing the coil, the rotor cup rotates one end of the spring to windthe spring tight around the shaft. The coil may be de-energized whilethe magnetic pull of the magnet applies a bias force to the spring tangthrough the rotor cup (Step 630). In this regard, the wound spring locksthe shaft while the permanent-magnet pull from the rotor cup maintains aconstant biasing force on the spring to keep the shaft locked after thecoil has been de-energized. The EMA may be de-energized and the retainedEMA load may be transferred from the motor assembly to the spring (Step640). In response to a command to disengage the park brake, the coil maybe energized to rotate the spring tang in the opposite direction todisengage the shaft and rotate the rotor cup assembly to a positionwhere the magnetic pull from the magnet applies an opposing bias forceto the spring tang after the coil has been de-energized (Step 650).

In various embodiments, the park brake mode may be activated to hold avehicle (e.g., an aircraft in a stationary position when the aircraft isat rest (e.g., during overnight storage). The park brake mode may beactivated to hold a vehicle stationary during a start, warm-up,inspection or service. The park brake mode may also be activated duringflight in an aircraft application to avoid vibrational wear to EMA 10and/or other brake system components.

In various embodiments, park brake systems described herein may provideoverall cost savings as compared to typical park brake systems.Moreover, the park brake systems described herein may occupy asubstantially reduced size envelope and mass of typical park brakesystems.

In various embodiments, while the park brake systems described hereinhave been described in the context of aircraft applications; however,one will appreciate in light of the present disclosure, that the parkbrake assemblies described herein may be used on various other vehiclessuch as, for example, trains. Moreover, the park brake systems describedherein may be employed with any suitable electric motor actuator in anyinstallation to create a bi-stable locked condition.

Thus, in various embodiments, the park brake systems described hereinprovide a cost effective, reliable, bi-staple locking system forelectric motor actuators.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the inventions. The scope of the inventions is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, C” is used inthe claims, it is intended that the phrase be interpreted to mean that Aalone may be present in an embodiment B alone may be present in anembodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Different cross-hatching is used throughout the figures to denotedifferent parts but not necessarily to denote the same or differentmaterials.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment”, “an embodiment”, “anexample embodiment”, etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is to be construed under theprovisions of 35 U.S.C. 112, sixth paragraph, unless the element isexpressly recited using the phrase “means for.” As used herein, theterms “comprises”, “comprising”, or any other variation thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or apparatus that comprises a list of elements does notinclude only those elements but may include other elements not expresslylisted or inherent to such process, method, article, or apparatus.

What is claimed is:
 1. A park brake system, comprising: a rotor cup; amagnet operatively coupled to the rotor cup; a stator configured toactuate the magnet in response to an input; a spring having a first endand a second end, the second end operatively coupled to the rotor cup;and a shaft, the spring installable around the shaft.
 2. The park brakesystem of claim 1, wherein the park brake system is installed in anelectric motor actuator.
 3. The park brake system of claim 2, whereinthe first end of the spring is operatively installed in an actuatorhousing.
 4. The park brake system of claim 3, wherein the rotor cup isinstallable within the housing.
 5. The park brake system of claim 3,wherein rotor cup is rotatable with respect to the housing.
 6. The parkbrake system of claim 5, wherein in response to the input the rotor cupis rotated causing the spring to tighten on the shaft.
 7. The park brakesystem of claim 1, wherein the stator comprises a coil assembly that isenergized in response to the input.
 8. The park brake system of claim 7,the stator comprises north pole teeth and south pole teeth, and inresponse to the coil being energized a first flux from at least one ofthe north pole teeth and the south pole teeth interact with a secondflux from the magnet.
 9. The park brake of claim 1, further comprising afirst mechanical stop and a second mechanical stop, wherein the firstmechanical stop and the second mechanical stop defines a rotationalrange of the rotor cup.
 10. An electric motor actuator, comprising: ashaft; a spring installable on the shaft, the spring comprising a firstspring tang and a second spring tang; a rotor cup rotatably installedabout at least a portion of the shaft, the rotor cup configured toreceive the second spring tang; a magnet coupled to the rotor cup; astator comprising a coil, wherein the rotor cup rotates in response tothe coil biasing the magnet, and wherein the spring tightens on theshaft in response to the rotor cup rotating.
 11. The electric motoractuator of claim 10, further comprising a housing configured to receivethe first spring tang.
 12. The electric motor actuator of claim 11,wherein the rotor cup is installable in the housing and wherein therotor cup is rotatable with respect to the housing.
 13. The electricmotor actuator of claim 10, wherein the rotor cup is configured tosurround at least a portion of the shaft.
 14. The electric motoractuator of claim 10 wherein the stator comprises a plurality of poleteeth, wherein a first portion of the plurality of pole teeth areconfigured to emit a first flux in response to a first condition andwherein a second portion of the plurality of pole teeth are configuredto emit a second flux in response to a second condition.
 15. Theelectric motor actuator of claim 10, wherein the coil is energized inresponse to a load on the electric motor actuator being above apredetermined threshold.
 16. The electric motor actuator of claim 15,further comprising a first mechanical stop and a second mechanical stop,the first mechanical stop and the second mechanical stop installed inthe electric motor actuator to prevent the magnet from reaching amagnetically stable condition.
 17. A method, comprising: monitoring anelectric motor actuator; detecting a load on the electric motoractuator; energizing a coil assembly in response to the load being abovea predetermined threshold; and actuating a rotor cup in response toenergizing the coil assembly, wherein a spring constricts a shaft tolock the electric motor actuator.
 18. The method of claim 17, whereinthe predetermined threshold is time.
 19. The method of claim 17, whereinthe spring is a wrap spring installed on the shaft.
 20. The method ofclaim 17, wherein energizing the coil actuates a magnet that is coupledto the rotor cup causing the rotor cup to rotate.